Optimum Propeller Positioning and Sizing for Underwater Vehicles

Miller, Lakshmi Madhavan (Virginia Tech) | Brizzolara, Stefano (Virginia Tech)


Propeller-hull interaction may have a relevant role in the overall propulsion efficiency of an underwater vehicle (UV) driven by single propeller: the modification of the boundary layer characteristics at the stern due to the momentum introduced in the flow by the propeller may determine a significant relative change of the hull drag and determine a very different effective inflow to the propeller, with respect to the bare hull condition. These effects are exacerbated for the current size Autonomous UVs (AUVs) whose cruising speed is kept low to increase range and endurance. Knutsson and Larsson (2011) studied different longitudinal positions of a large diameter propeller in the stern of a singlescrew tanker. While they demonstrated the general principle that larger propeller diameters and larger longitudinal clearances may lead to higher propulsion efficiencies, in their study, the propeller design was kept fixed. Changing position and diameter of the propeller, obviously changes the self-propulsion coefficients, but it also changes the nominal wake at the propeller disk. Eslamdoost et al. (2017) performed a CFD study on the effect on hull-propeller interactions with varying propeller diameters. However, they used the same design of propeller which remained un-optimized in terms of open water efficiency, pitch and RPM for each of these cases. Conceptually, when the propeller gets a larger diameter and it is moved further downstream from the underwater vehicle tail, the hull efficiency initially increases and then start decreasing again (the thrust deduction at first decreases more rapidly than the decrease of wake fraction).